1. Field of the Invention
This invention relates in general to a well drilling apparatus and in particular to a top drive well drilling apparatus.
2. Description of the Prior Art
A top drive drilling system rotates a drill string from the top, rather than using a rotary table, a kelly, and a kelly bushing. An electric drilling motor is suspended from the drilling rig's conventional swivel and is attached to the top of the drill string. The drilling motor may also be attached to a carriage, which is guided by a pair of vertical tracks. The drilling motor is connected to the drill string by a cylindrical stem, which extends downward from the motor. A wrench assembly is also suspended from the drilling motor, in order to break out or make up connections between the stem and the drill string. A drill pipe elevator is suspended by links below the bottom of the stem. As the drill string is drilled down, the elevator will contact the floor of the drilling rig. If the elevator and the wrench assembly could be moved out of the way, the drill string could be drilled down further before additional lengths of pipe must be added to the drill string.